i used to own a suzuki samurai that had an issue like that, sounded more like sand paper grinding together tho......possible a bearing in your reverse gear shaft in your tranny? idk how the taco transmissions work yet, havent really tore into one but i would assume the fundamentals are still the same.

another possability would be it might be comming from your rear diff? or t-case? the u-joints are near both of those, so it may be kind of hard to figure out.